The present invention relates to a hydraulic valve of an internal combustion engine, wherein the hydraulic valve is configured to limit flow during, for example, locking of a cam phaser of an internal combustion engine. More specifically, the hydraulic valve can be employed in connection with the cam phaser and locking system which is disclosed in U.S. patent application Ser. No. 13/624,196.
A typical internal combustion engine provides that a crankshaft drives a drive wheel using a chain or drive belt. A stator is joined in a torsionally rigid manner to the drive wheel. As such, the stator is drive-connected to the crankshaft by means of this drive element and drive wheel.
A corresponding rotor is engaged with the stator, and is joined to the camshaft in a torsionally rigid manner. The camshaft has cam lobes thereon which push against gas exchange valves in order to open them. By rotating the camshaft, the opening and closing time points of the gas exchange valves are shifted so that the internal combustion engine offers its optimal performance at the speed involved.
To optimize performance during operation of the internal combustion engine, the angular position of the camshaft is continuously changed relative to the drive wheel depending on the relative position of the rotor relative to the stator. Specifically, the engine RPM and the amount of torque and horsepower the engine is required to produce are the bases for the timing adjustments. These adjustments take place while the engine is in operation. This makes variable valve timing possible because intake and exhaust valve timing is constantly adjusted throughout the RPM range. The performance benefits include the increase of engine efficiency and improvement of idle smoothness. The engine can also deliver more horsepower and torque versus a similar displacement engine with conventional valve timing. This also allows the engine to have improved fuel economy and results in the engine emitting fewer hydrocarbons.
The stator includes webs which protrude radially toward a central axis of the stator. Intermediate spaces are formed between the adjacent webs, and pressure medium is introduced to these spaces via a hydraulic valve. The rotor includes vanes which protrude radially away from the central axis of the rotor, and project between adjacent webs of the stator. These vanes of the rotor subdivide the intermediate spaces between webs of the stator into two pressure chambers (often referred to as “A” and “B”, respectively). In order to change the angular position between the camshaft and the drive wheel, the rotor is rotated relative to stator. For this purpose, depending on the desired direction of rotation each time, the pressure medium in every other pressure chamber (“A” or “B”) is pressurized, while the other pressure chambers (“B” or “A”) are relieved of pressure toward the tank.
During some operating states of the internal combustion engine, it becomes imperative to lock the position of the rotor relative to the stator. For this purpose, a valve timing control apparatus in the form of a lock pin may be utilized on the rotor for locking into a corresponding bore which is provided in the stator.
The locking pin of many cam phase locking systems provides that the locking pin is held in the unlocked position by the pressure of one chamber. If a stepped locking pin is utilized, pressure might also come from both chambers because the “step” of the stepped locking pin separates both chambers from each other.
Typical problems that occur in a cam phase locking system include, but are not limited to:                failure to lock or inefficient locking when the pressure medium is cold;        residual pressure in the retard and/or advance chamber (due to torque reversals of the camshaft (possibly caused by spring forces of the gas exchange valves)) tends to unlock the pin, especially when the engine-ignition is switched off but the crankshaft still rotates;        failure to lock or inefficient locking when the engine is turned off; and        when pressure medium gets hot sometimes it leaks, causing the pump to deliver less pressure, which influences the cam phasers as well as the operation of the lock pin, wherein there may be a failure to lock or inefficient locking due to low pressure medium pressure.        
During locking of a cam phaser, it is important to limit the flow of pressure medium in order to improve the pressure differential across the phaser. On the other hand, if full flow were allowed, the system would move too quickly and become unstable. If the hydraulic resistance of the hydraulic valve were zero (i.e., unrestricted), then the pressure in both sides of the phaser would be equal to the supply pressure. In this case, there would be no force and no torque to move the phaser in either direction regardless of how much flow was drained from one side of the phaser, such as from either side of the centering slot which is disclosed in U.S. patent application Ser. No. 13/624,196.
The bottom line is that flows from a hydraulic valve must be restricted in order to generate phaser torque, and the torque is greatest when the hydraulic valve flows are matched between the two conditions of the phaser centering slot paths. The present invention provides a method of using a hydraulic valve to limit flow to a cam phaser during locking, thereby damping the system.